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Limit number of concurrent DNS queries

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Signed-off-by: Santhosh Manohar <santhosh@docker.com>
This commit is contained in:
Santhosh Manohar 2016-03-28 16:23:08 -07:00
parent 9ca3964233
commit bd0d8222aa
1 changed files with 41 additions and 1 deletions
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42
libnetwork/resolver.go
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@ -47,6 +47,8 @@ const (
maxExtDNS = 3 //max number of external servers to try
extIOTimeout = 3 * time.Second
defaultRespSize = 512
maxConcurrent = 50
logInterval = 2 * time.Second
)
type extDNSEntry struct {
@ -64,6 +66,9 @@ type resolver struct {
tcpServer *dns.Server
tcpListen *net.TCPListener
err error
count int32
tStamp time.Time
queryLock sync.Mutex
}
func init() {
@ -162,6 +167,9 @@ func (r *resolver) Stop() {
r.conn = nil
r.tcpServer = nil
r.err = fmt.Errorf("setup not done yet")
r.tStamp = time.Time{}
r.count = 0
r.queryLock = sync.Mutex{}
}
func (r *resolver) SetExtServers(dns []string) {
@ -328,7 +336,8 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
if extDNS.ipStr == "" {
break
}
log.Debugf("Querying ext dns %s:%s for %s[%d]", proto, extDNS.ipStr, name, query.Question[0].Qtype)
log.Debugf("Query %s[%d] from %s, forwarding to %s:%s", name, query.Question[0].Qtype,
w.LocalAddr().String(), proto, extDNS.ipStr)
extConnect := func() {
addr := fmt.Sprintf("%s:%d", extDNS.ipStr, 53)
@ -366,6 +375,15 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
extConn.SetDeadline(time.Now().Add(extIOTimeout))
co := &dns.Conn{Conn: extConn}
if r.concurrentQueryInc() == false {
old := r.tStamp
r.tStamp = time.Now()
if r.tStamp.Sub(old) > logInterval {
log.Errorf("More than %v concurrent queries from %s", maxConcurrent, w.LocalAddr().String())
}
continue
}
defer func() {
if proto == "tcp" {
co.Close()
@ -373,11 +391,13 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
}()
err = co.WriteMsg(query)
if err != nil {
r.concurrentQueryDec()
log.Debugf("Send to DNS server failed, %s", err)
continue
}
resp, err = co.ReadMsg()
r.concurrentQueryDec()
if err != nil {
log.Debugf("Read from DNS server failed, %s", err)
continue
@ -397,3 +417,23 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
log.Errorf("error writing resolver resp, %s", err)
}
}
func (r *resolver) concurrentQueryInc() bool {
r.queryLock.Lock()
defer r.queryLock.Unlock()
if r.count == maxConcurrent {
return false
}
r.count++
return true
}
func (r *resolver) concurrentQueryDec() bool {
r.queryLock.Lock()
defer r.queryLock.Unlock()
if r.count == 0 {
return false
}
r.count--
return true
}